Brawl Stage Studio is a PC stage builder for Nintendo's latest installment in the Smash series: Super Smash Brothers Brawl.
It offers many new features not possible with Brawl's build-in Stage Builder like placing up to 252 blocks, loading custom stage preview images,
having access to the beta block, placing spawn points and many more.
Use you Wii SD card and import/export your custom stages.

Dolphin users:How do i import my custom stages from sd.raw (Dolphin) for BSS?
1st Download WinImage or a similiar program (that let's you manage virtual drives)
2nd With it, open your sd.raw
3rd Now like a sd card, go to -> private -> wii -> app -> rsbp -> st
4th Now create your stage and inject it in this directory
5th Now play with it